Beyond Silicon: A Look at Alternative Semiconductor Materials

Solutions for Extreme Environments

Wide-bandgap semiconductors are a class of materials that offer a range of advantages over silicon. These materials can operate at higher voltages and temperatures, serving as critical enablers of innovation by opening up higher communication channels and functioning in a wider range of environments that are sometimes extreme. Electronics applications in power and RF can benefit from these wide-bandgap materials by allowing for faster, smaller, more efficient, and more reliable device designs.

Two prominent wide-bandgap semiconductor materials in use today are gallium nitride (GaN) and silicon carbide (SiC). Both materials came to commercial prominence in the late 1980s with the development of blue LEDs and were made possible because of the size of their bandgap. (Bandgap is the distance between the valence band of electrons and the conduction band.) Advances in GaN growth processes over SiC ultimately led to its widespread adoption in optical technologies, such as Blu-ray DVD players, and resulted in a Nobel Prize in Physics in 2014.  

Besides having a wide bandgap, these materials also have a very high thermal conductivity which means they can dissipate heat more effectively which results in more efficient devices as lower temperatures optimize device performance. The ability to withstand higher electric fields and high temperatures makes these materials particularly attractive in power electronics applications, especially for the design of inverters, power supplies, and motor drives. Automotive applications such as electric vehicles (EVs) and plug-in, hybrid vehicles benefit greatly from the characteristics that GaN and SiC bring to power devices.

In addition to its application in LEDs and power electronics, GaN is also an important material in high-frequency devices like RF amplifiers and has led to improvements in wireless communication and 5G networks.

Meanwhile, SiC is a very hard material and possesses a high mechanical stability. Combined with its low material cost, SiC is valuable in many different industries, including for abrasive and cutting tools.

High Potential, High Complexity

Of course, many aspects of developing GaN and SiC for use in the semiconductor industry are more complex than traditional silicon. The main issues standing in the way of GaN's widespread adoption are its reliability and cost.

While GaN's 3.4eV (versus silicon's 1.12eV) bandgap makes it well-suited to high-power and high-frequency devices, it is prone to defects and dislocations during the growth process and device reliability can be problematic. This also makes it difficult and very expensive to grow large GaN-based wafers. To overcome this, many researchers’ focus on developing ways to integrate GaN onto silicon wafers, which means bringing two different crystal structures together in a way that avoids dislocations and defects. It is no easy task and often leads to wafer cracking.

As for SiC, its characteristics (namely its hardness and its fragility) make it challenging to produce. The material needs higher temperatures as well as a lot of time and energy for the crystal to grow and be processed. Surface defects can be challenging to find during inspections, especially with the widely used 4H-SiC crystalline structure, which is noted for its high transparency and high refractive index.